Abstract

The Borneo marine Research Institute (BMRl) UMS embarked on a stock enhancement programme of the Maaobrachium rosenbergii(giant freshwater prawn) in an attempt to replenish stocks in Petagas River, Sabah. In rivers, phytoplankton is crucial for biogeochemical cycles and forms the base of food chains and food webs in every aquatic ecosystem. The purpose of this study was to investigate the species abundance and diversity of phytoplankton in Petagas River and their relationships with the postIarvae (PL) of the giant freshwater prawn, Macrobrachium sp., salinity,
and water quality of Petagas River. A phytoplankton net and Van Dam Water Sampler were used to collect qualitative and quantitative phytoplankton samples, respectively, from five sampling stations. Samples collected were preserved with
Lugol's solution, stored and labelled. The samples were examined, counted and identified using the Sedgwick-Rafter counting cell under a compound. The Pollution Index method by Palmer (1969) was used to determine the level of organic pollution of the Petagas River within the study area. Results obtained showed that a total of 48 species of phytoplankton belonging to 34 genera from 5 Division were recorded. The species identified were from the divisions Badllariophyta (21), Chlorophyta (16), Cyanophyta (5), Dinophyta (2) and Euglenophyta (4). Chlorella sp., Scenedesmus quadricauda, Coelastrum microsporum, Crudgenia lauterbonii and Osdllatoria sp. were the dominant species. Diversity based on Shannon-Wiener diversity index (H')
showed a higher value during the wet season compared to dry season, although total phytoplankton abundance were higher during the dry season, due to prevalence of red tide season. The results also showed that the presence of PL is negatively correlated to the total cell abundance of phytoplankton, while salinity showed positive correlation to species diversity and abundance of phytoplankton in Petagas River. The study revealed that Petagas River is contaminated with high organic pollution, which may be due to increasing population and human-interaction activities. The outcome of this study suggests that phytoplankton can be used as bioindicator species to monitor the river water quality in terms of organic pollution in Petagas River.